The present invention relates generally to the preparation and delivery of dental amalgam and relates more particularly to a method and apparatus wherein the amalgam constituents are stored and mixed in, and delivered from, a sealed capsule.
Dental amalgams conventionally include an alloy of various metals in powdered form which is mixed with mercury just prior to application to a prepared dental cavity. In early dentistry, the amalgam ingredients were mixed in an open vessel and the proportions were gauged by the viscosity of the mixture. As dental techniques improved, it was recognized that more careful attention to the proportions of the ingredients was desirable and systems were devised whereby the amalgam ingredients were prepackaged in capsules in the correct proportions. Transfer from prepackaged capsules to the mouth still involved the use of open vessels with the opportunity of contamination of the amalgam by foreign matter and bacteria, and contamination of the environment by spillage and vaporization of mercury.
The belated recognition of the toxic nature of mercury vapors and the dangers inherent in any procedure which permit the exposure of the mercury or the amalgam to the atmosphere has resulted in the proposal of a number of systems for storing, mixing and dispensing the amalgam to minimize such exposure.
In U.S. Pat. No. 1,774,258, for example, a capsule is provided having separate compartments within which the amalgam ingredients may be separately stored. When the amalgam is needed, the membrane separating the compartments is broken and the mixing of the ingredients is accomplished by placing the capsule in a mixing machine. For delivery to a patient, however, the amalgam must be placed in an open container for pickup by an amalgam applicator and hence this particular approach eliminates only a part of the problem, namely the proportioning of the ingredients and the isolation thereof from the atmosphere during storage and mixing. Other forms of capsules for storing and mixing of dental materials are shown in U.S. Pat. Nos. 2,527,991 and 3,638,918.
Later developments recognized the desirability of dispensing the amalgam directly from the container in which it was mixed into the prepared dental cavity. Patents exemplifying such a system include U.S. Pat. Nos. 3,368,592, 3,521,356, 3,724,077 and 3,828,434. In none of these arrangements, however, does it appear that the amalgam constituents are packaged and stored in the container in which the mixing takes place.
More recent developments have attempted to combine the storage, mixing and delivery functions in the same container or capsule. For instance, in U.S. Pat. No. 3,760,503 the ingredients are brought together by the puncturing of the compartment holding one component by a spatula which is then rotated to mix the ingredients. When mixing is completed, the spatula is withdrawn and a plunger inserted to deliver the mixture from the opposite end of the container.
U.S. Pat. No. 4,084,320, discloses a structurally complex capsule having rotatable and removeable end members which are rotated to provide communication of the mercury with the powder materials, again rotated to provide a mixing of the materials, and then removed and replaced by special spout and plunger elements for delivery of the amalgam.
Although various types of capsule systems have been made commercially available, they have not, for various reasons, become popular, and dentists today are still to a large extent using techniques which involve the placement of the amalgam on an open surface for piecemeal transfer to the cavity in an amalgam carrier. Not only do such techniques permit the release of toxic mercury vapors, but they also permit contamination of the amalgam by exposure to contaminents on the surface, in the air, and especially in the amalgam carrier which is repeatedly exposed to the bacteria of different patients' mouths.